Photographic emulsions and developers stabilized with purine compounds



United States Patent PHOTOGRAPHIC EMULSIONS AND DEVELOPERS STABILIZED WITH PURINE COMPOUNDS Fritz Dersch and Millet R. De Angelus, Binghamton,

N. assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 23, 1958, Ser. No. 769,063 11 Claims. 01. 96-66) The present invention relates to the use of antifogging and stabilizing agents for photographic silver halide emulsions and, particularly, to the use of carboXya1kyl-6- purinyl thioethers and their salts and esters for such use.

It is Well known in the photographic art that lightsensitive emulsions, such as gelatino silver halide emulsions, have a tendency to fog. a prolonged ripening of the emulsions, by prolonged storage especially at elevated temperatures and humidity, and by prolonged development. To overcome this undesirable property, it has been the practice in this art to add certain chemical compounds to the emulsions to increase their stability and to reduce their tendency to fog. However, all stabilizing and antifogging compounds heretofore used in this art have the disadvantage that upon addition to the emulsion they cause a loss of speed and/ or contrast of the emulsion.

It is, accordingly an object of this invention to pro duce a light-sensitive emulsion which is fast, stable, has a reduced tendency to fog and has good contrast.

A further object of this invention resides in a lightsensitive emulsion which contains a compound which stabilizes the emulsion against fogging and at the same time does not materially reduce the speed and/or the contrast of the emulsion.

A still further object of this invention is to provide Fog is usually caused by j bromo acetic acid,

Examples of compounds within the ambit of such formula which we have found to be elfective are:

6-carboxyethylthiopurine The sodium, potassium, ammonium or silver salt of 6- carboxyethylthiopurine The methyl, ethyl or phenyl ester of 6-carboxyethylthiopurine -carboxypropylthiopurine The methyl, ethyl or phenyl ester of 6-carboxypropylthiopurine 6-carboxymethylthiopurine and its sodium or potassium salts The above compounds may be prepared by refluxing a 6-mercaptopurine with a brornoaliphatic' acid such as B-bromo propionic acid or -bromo b-utyric acid in the presence of an acid binding agent such as sodium hydroxide, pyridine, trimethylainine or the like. Conversely, those compounds in which the sulfur atom is joined to the carboxy group through ethyl or propyl may be prepared by heating an aqueous solution of 6-mercaptopurine in an acid binding agent such as sodium hydroxide with fl-propiolacetone on the one hand or 'y-butyrolactone on the other hand.

The free acid produced by the above methods may be converted to its salt by a reaction With a compound a light-sensitive emulsion containing a compound which stabilizes the emulsion against fogging and at the same time does not appreciably reduce the sensitivity to light of longer wave length effected by the presence of sensitizing dyes.

Other objects and advantages of this invention will appear to those skilled in the art from the detailed description thereof given below.

We have discovered that the class of compounds having the following general formula, when added to a lightsensitive silver halide emulsion, stabilize "and inhibit the fogging of the emulsion:

S-(GHz) 11-0 0 O R containing the desired cation such potassium carbonate, silver nitrate, ammonium carbonate or the like.

, If esters are desired, they may be produced in the conventional manner by refluxing the free acid with the desired alcohol or phenol in the presence of hydrochloric acid.

The antifogging agents of our invention may be added to the emulsion at any stage during its process of production. Thus, they may be added as a ripening final or as a coating final. When added as a ripening final, they are added during the ripening or sensitivity increasing stage of the emulsion making process. Such addition may be made before, during or after the addition of the soluble silver salt to the soluble halide in the presence of a suitable colloid, such as gelatin, polyvinyl alcohol, solubilized casein or albumin. When added as a coating final, the antifogging agent of our invention is added to the emulsion just prior to coating it on a suitable support such as glass, paper or film at a time when the emulsion has nearly attained its maximum sensitivity.

In some instances, it is advantageous to apply the antifogging and stabilizing compounds of our invention in a separate layer such as an undercoating layer or in an antiabrasion gelatin surface. Sometimes it is desirable toincorporate the compounds in one or all processing baths or in the preand post-baths.

'When used as a ripening final, the antifoggantsof our invention are preferably added to the emulsion in an amount ranging from 1 milligram to 25 milligrams per 0.6 mol of silver halide and when used as a coating final they are preferably added in an amount ranging from 10 also be used in combination with known antifoggants and a stabilizers. The antifoggants of our invention can also be used in combination with sensitizers such. as sulfur,

metal and reduction sensitizers as well as with accelerators such as the polyoxyethylenes (see U.S.P. 1,970,578)

and their derivatives and polyvinyl-pyrrolidone.

The novel antifoggants of our invention may be used.

with various types of photographic emulsions, such as as sodium carbonate,

non-sensitized orthochromatic, panchromatic and X-ray emulsions, paper emulsions and color emulsions.

Example I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents. A 1 solution of 6-carboxy-ethylthiopu-rine was added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained about 0.6 mol of a silver halide. The so-prepared emulsion samples were coated on a suitable Cellulose ester base and dried. Samples of these film coatings were then exposed in a Type 113 Sensitometer, and developed in a developer of the following composition:

Grams N-methyl-p-aminophenol 1.5 Sodium sulfite, anhydrous 45 Sodium bisulfite Y 1 Hydroquinone 3 Sodium carbonate, monohydrated 6 Potassium bromide .8 Water to make 1 liter.

The results obtained were as follows:

Quantity of Compound Relative Fog at 12 Oven Fog at Used Speed Develop- 6' Development ment The stabilizer was prepared as follows: 5 grams of -mercaptopurine were dissolved in a 35 ml. aqueous solution containing 2.0 grams of NaOH. 2.88 grams of fi-propiolaotone were slowly added to this solution with constant stirring, the temperature of the reaction during addition being maintained under 50 C. The reaction was allowed to run three hours at steam bath temperature. After cooling to room temperature, the reaction mixture was acidified with concentrated HCl to pH 2 and chilled in an ice bath. The precipitate was collected and crystallized twice from ethanol using water to initiate the crystallization. 3 grams of the white product were obtained melting at 219-220 C. (uncorrected).

Example II The procedure was the same as that of Example I excepting that there was used 6-carboxypropylthiopurine as the stabilizer. The results were similar to those of Example I.

The 6-carboxypropylthiopurine was prepared in the same manner as the compound used in Example I excepting that the fi-propiolactone was replaced by 'y-butyrolactone.

Example Ill The" procedure was the same as that of Example I excepting that the 6-carboxyethylthiopurine was replaced by o-carboxymethylthiopurine.

The 6-carboxymethylthiopurine was obtained by refluxing" for several hours molecular quantities of G-mercaptopurine and bromo acetic acid in the presence of aqueous sodium hydroxide. After cooling, the reaction mixture was acidified with dilute hydrochloric acid, chilled and filtered.

Example lV Exposed samples of a photographic film were developed for twelve minutes at 65 F. in a standard N-methyl-paminophenol-hydroquinone developer. Two testswere made, one with the normal developing solution and one with a developer containing 100 mgs. of 6-carboxyethyl- A thiopurine per one liter of developer. Sensitometric strips, developed in the normal developer (control) for twelve minutes showed a fog of .30, whereas those strips which were developed in the developer containing the antifoggant had a fog of .20.

Modifications of the invention will occur to persons skilled in the art. It is evident that in lieu of the antifoggant of the examples, we may use any of the antifoggants mentioned above. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion, said light-sensitive material containing as an antifoggant a compound of the following formula:

S-(CHnr-OOOR where R is selected from the group consisting of hydrogen, an aliphatic radical, aralkyl, aryl and a cation and n represents a whole number of from 1 to 3.

2. A light-sensitive silver halide emulsion containing an antifog'gant and stabilizing compound having the folwherein R is selected from the group consisting, of hydrogen, an aliphatic radical, aralkyl, aryl and a cation and n represents a whole number of from 1 to 3.

3. A light-sensitive silver halide emulsion containing 6-carboxyethylthiopurine as an antifoggant and stabilizer.

4. A light-sensitive silver halide emulsion containing 6-carboxymethylthiopurine as an antifoggant and stabilizer.

5. A light-sensitive silver halide emulsion as recited in claim 2 wherein the antifogging and stabilizing compound is present in the emulsion in the ratio of 1 to 300 milligrams per 0.6 mol of silver halide.

6. A light-sensitive silver halide emulsion as recited in claim 2 wherein the antifogging and stabilizing compound is present in the emulsion in the ratio of 1 to 25 milligrams per 0.6 mol of silver halide.

7. A light-sensitive silver halide emulsion as recited in claim 2. wherein the antifogging and stabilizing com pound is present in the emulsion in the ratio of 10 to 300 milligrams per 0.6 mol of silver halide.

8. An N-methyl-p-aminophenol-hydroquinone developing solution containing a compound having the following general chemical formula! 5 10. In a process of developing an exposed silver halide emulsion, the step which comprises developing said emulsion with an N-methyl-p-aminophenol-hydroquinone developing solution in the presence of an antifogging and stabilizing compound having the following general formula:

wherein R is selected from the group consisting of hydrogen, an aliphatic radical, aralkyl, aryl and a cation and n represents a Whole number of from 1 to 3.

11. A process as recited in claim 10 wherein the antifogging and stabilizing compound is 6-carboxyethylthiopurine.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC MATERIAL COMPRISING A BASE AND A LIGHT-SENSITIVE SILVER HALIDE EMULSION, SAID LIGHT-SENSITIVE MATERIAL CONTAINING AS AN ANTIFOGGANT A COMPOUND OF THE FOLLOWING FORMULA: 